The present invention relates to a protecting device to be provided, for example, between an on-vehicle power source and an on-vehicle electric load, for cutting off power supply from the power source to the on-vehicle electric load on such an occasion as inspection of the load.
When executing maintenance services for various electric products like a radio or navigation system mounted on a vehicle it is not desirable to perform work while a voltage from a battery remains applied to the appliances.
In other words, from the viewpoint of safety it is desirable to isolate all the electric products from the power source prior to executing the maintenance work, for instance, by disconnecting from the power source wires that are directly connected to the power source such as a battery etc.
Accordingly, such techniques have recently been developed as providing close to a power source a protecting device comprising terminals in mutual contact that can be separated for disconnecting the power supply to each electric load, so that when executing maintenance work the terminals of the protecting device can be separated to cut off the power supply to each load.
In the protecting device that cuts off the power in the proximity of the battery as above, the terminals are tend to being damaged due to an arc that flies when separating the terminals because the power is relatively great. Especially, batteries recently have a higher rated voltage, creating an increasing demand for a technique to prevent damage to terminals due to arcing.
In view of the foregoing problem in the prior art, the invention provides a protecting device that produces an arc when isolating an electric load from the power source at a different point from the terminals for connecting the power source and the electric load, so that the terminals can be protected.
The present invention provides a protecting device comprising a fixed member to be fixed on a vehicle and a movable member that can be attached to or removed from the fixed member for cutting off power supply from an on-vehicle power source to each electric load by removing the movable member from the fixed member, wherein the fixed member is provided with an input terminal connected to the on-vehicle power source and an output terminal connected to each electric load; the movable member is provided with a first current pass that has movable side connecting terminals on its ends to be respectively connected to the input terminal and the output terminal in a state where the movable member is attached to the fixed member; the fixed member is also provided with a second current pass connecting the input terminal with the output terminal separately from the first current pass; the second current pass is provided with terminal protecting contacts during midstream that can make mutual contact; further, means for switching current is provided for breaking a current on the second current pass in a state where the movable member is attached to the fixed member and passing a current through the second current pass in a state where the movable member is removed from the fixed member but before the input terminal and the output terminal are separated from the movable side connecting terminals; and the terminal protecting contacts make mutual contact in a state where the movable member is attached to the fixed member and separate from each other in a state where the movable member is removed from the fixed member but after the current switching means has switched the second current pass from off to on.
In this device, in a state where the movable member is attached to the fixed member with the input terminal and the output terminal respectively connected to the on-vehicle power source and to each of the electric loads, the input terminal and the output terminal are connected through the first current pass on the movable member, enabling power supply to each of the electric loads. At this stage the terminal protecting contacts are mutually contacting, however, since the second current pass is disconnected by the current switching means the power is being supplied exclusively through the first current pass.
Upon starting a removing action of the movable member under this state, first the current switching means turns on the second current pass, therefore the power source and the electric loads are connected through both the first current pass and the second current pass. Then the movable side connecting terminals are separated from the input terminal and the output terminal so that the first current pass becomes disconnected, however, at this moment an arc will not fly between the input and output terminals and the movable side connecting terminals since the power source and the electric load remain connected through the second current pass, therefore these terminals are effectively protected. Following this the terminal protecting contacts separate from each other, at which time an arc will fly between the terminal protecting contacts in a case where the power is large.
Accordingly, if an arc ever flies it is only between the terminal protecting contacts, and since an arc will not fly between the input and output terminals and the movable side connecting terminals, these terminals are securely protected. Consequently the device also provides a solution for increasing voltage of the power source.
Here, it is preferable that the terminal protecting contacts are made of a material that has a greater arc resistance than the input terminal and the output terminal. As a result the terminal protecting contacts can be used for a prolonged period with less frequency of maintenance work. Also, materials with a greater arc resistance, for example, Agxe2x80x94CdO family materials, Agxe2x80x94Ni family materials, Ag-metal-oxide family materials, Agxe2x80x94Gr family materials, etc., have a greater resistance than materials generally used for electric connection such as copper, however, since the second current pass is disconnected by the current switching means so that power is supplied to each electric load exclusively through the first current pass in a state where the movable member is attached to the fixed member, a greater resistance of the terminal protecting contacts will not cause any disturbance with the power supply.
Further, it is also preferable to provide a condenser in parallel with the terminal protecting contacts, because arc discharge between the terminal protecting contacts can be restrained by a condensing effect of the condenser, and resultantly the life span of the contacts can be prolonged. In this case also, since the second current pass including the condenser is disconnected by the current switching means while the power is supplied to each electric load, there will be no disturbance in the power supply.
Regarding the configuration for connecting the terminal protecting contacts, it is preferable to dispose the contacts on elastically deformable spring pieces formed in such a manner that the terminal protecting contacts remain separated in a natural state where an external force is not subjected to the spring pieces, and to provide an operating section on the movable member that forces the terminal protecting contacts to contact with each other in a state where the movable member is attached to the fixed member.
By a construction, the terminal protecting contacts will remain separated due to the natural shape of the spring pieces in a state where the movable member is not attached to the fixed member. And once the movable member is attached to the fixed member the operating section will cause an elastic deformation of each spring piece, thus forcing the terminal protecting contacts to contact with each other.
Further, it is preferable that the current switching means comprises of a pair of current switching terminals that are separated and included in the second current pass and a connecting conductor located on the movable member that becomes separated from at least one of the current switching terminals in a state where the movable member is attached to the fixed member but that contacts with both of the current switching terminals at least in a state where the terminal protecting contacts are separated from each other, to achieve electric connection between the current switching terminals.
According to this configuration, current switching operation on the second current pass can be properly performed by a simple construction of only a pair of current switching terminals and a connecting conductor that can contact with and separate from the current switching terminals.